Good Point - Andrew Landers
Developing precision canopy sprayers
Left: An adjustable air outlet keeps the spray cloud in the trees. Right: Ultra sonic sensors determine absence, presence, or height
The use of pesticides on fruit crops has long been a point of concern to the discerning consumer. Spraying machines applying pesticides have also given rise to concern as they frequently create drift, which reduces efficiency, affects off-target crops and creates environmental pollution and operator contamination.
The challenge for Cornell University engineers is to develop a precision canopy sprayer that is able to adjust both application rate and air volume to match the growing canopy as the season progresses. In essence, we are applying the old principles of tree row volume to the modern world of real time sensors using electronics.
For the past decade researchers in the pesticide application group at Cornell University have been studying methods of addressing the necessary inputs and outputs for an automatic sprayer and are now set to develop such an integrated machine. After the Farm Bill was passed last summer, the U.S. Department of Agriculture awarded a $3.9 million grant for a three-year applied research project, known as the Integrated Automation for Sustainable Specialty Crop Farming Project, that will develop, test and evaluate robotic tractors and automatic sprayers so that human operators are not required. Colleagues at Carnegie Mellon University will develop a robotic tractor and other collaborators include the University of Florida and John Deere. Field evaluation will take place at Southern Gardens Citrus, one of Florida's largest citrus growers. Initially the project is for spraying orange groves, but the results will readily transferable to apple orchards and vineyards.
In the Finger Lakes region of New York, we are conducting trials with canopy sensors fitted to a vineyard sprayer. The sensors follow along the top and middle trellis wires and monitor canopy development as the season progresses. Early and mid-season uses have the greatest potential to reduce both drift and pesticide use.
At Cornell University, we have also conducted field trials for the past three years to evaluate the effect of changes in application volumes during the course of canopy development in vineyards. To account for changes in canopy volume and to find the optimum volume of pesticides to apply, a computer program, Dosavina was developed for New York growing conditions with visiting Professor Emilio Gil of Catalonia.
The software Dosavina is based on using different types of vineyard sprayers and adds a complete database about crop characteristics (such as structure, crop stage, leaf area, vine row volume, and leaf area index). The objective of this work has been to develop an easy and useful tool, able to determine the optimal volume rate to apply in vineyards.
The program includes the possibility to calculate the working parameters (pressure, nozzle type, and size) according to the recommendations obtained on volume rate and gallons per acre. Trials were conducted on nine varieties at vineyards belonging to three cooperating growers in New York State. Concentration of product remains the same in the tank, while volume rate per acre is adjusted.
Savings in pesticide use, particularly in early season, were quite substantial. Average seasonal savings in pesticide use over the three-year trial amounted to 34 percent.
Adjustment of air speed, direction and volume, is important. From 2001-2006, a series of sprayer tests were carried out at Cornell University to determine airflow characteristics of sprayers used in orchards and vineyards. Deflectors were developed for traditional sprayers and field tests showed a 20 to 30 percent improvement in deposition and, importantly, with equal deposition throughout the height of the canopy. Horizontal airflow, at reduced air volumes, gave the best results. Air speed and volume need to be adjustable to match the growth stage of the canopy. A number of simple methods to do this are available and include changing PTO speed, fitting an air limiting system to the air intake or outlet, or using a variable speed drive to the fan.
Changing PTO speed is the simplest method, providing the operator is aware of changes in engine torque on the tractor. Field trials conducted using an AgTec P300 sprayer fitted with airshear nozzles operating at two fan speeds, 2076 rpm (540 rpm PTO) and 1557 rpm (405 rpm PTO), showed that the lower PTO speed resulted in considerably less drift and increased deposition than the higher PTO speed.
Limiting the amount of air entering the sprayer is attainable by using a "Cornell doughnut" system. Simple doughnuts are made and fitted to the air intake and the intake hole changed (one-third, one-half, and two-thirds hole size) as the canopy develops. Field trials show considerable reduction in drift and improved deposition in grapevines.
We have conducted many trials with adjustable air outlets in apple trees and vines. For example, trials conducted with a Rears tower sprayer fitted with a louver to adjust the airflow showed that drift can be virtually eliminated and therefore deposition considerably improved. Using an adjustable airflow on a Croplands sprayer allowed an apple grower in Orleans County, New York, to apply spray from one side only in spindle trees all season with no fall off in pack-out quality. Spraying from one side allows the grower to halve tractor, operator, time, and fuel costs or alternatively double the workload of the tractor and sprayer.
In the automatic sprayer that is being developed, air will be adjustable according to wind direction across the orchard or vineyard. A sonic anemometer in conjunction with a GPS locator, will determine true wind-speed and direction. The air flow from the sprayer will increase air output on the upwind side of the sprayer to move spray into the canopy against the wind, and the down wind side could reduce airflow—all done automatically.
In Florida, scientists are developing a system for tractor automation in citrus groves that includes autonomous tractors and automatic canopy sprayers for spraying orange trees.
The question of canopy sprayer workrate arises when large areas of fruit crops are grown, and timeliness is of great concern. A small autonomous sprayer could travel to an individual tree or vine, apply pesticides and then return to a base, whereas when a whole orchard, grove or vineyard requires pesticide application, then multiple tractors with large volume sprayers are needed.
Much needs to be done to combine existing knowledge on canopy spraying in orchards and vineyards with existing knowledge on precision farming in field crops.
An automatic fruit sprayer is closer than we think if we choose to blend existing spraying research knowledge with proven technology. There exists a need for sprayer manufacturers to collaborate with researchers to develop such techniques if we are to remain competitive in a global market.
Current research at Cornell University is leading rapidly to the development of a precision canopy sprayer for the fruit industry.